2023-10-12 16:03:14
Foot and mouth disease is a highly contagious viral disease that affects more than 70 species of domestic and wild animals, notably cattle, pigs, sheep and goats. The virus is not transmissible to humans but causes considerable economic losses in the event of an infectious outbreak on farms. Even if the mortality rate induced by the disease remains relatively low, infected animals are weakened and spread the virus. It is mainly present in Africa, Asia, the Middle East and some countries in South America. Western Europe is free of the disease. The characterization of the strains circulating in the countries concerned is essential to fight against the disease: “ foot-and-mouth disease vaccines do not provide protection against multiple strains at once, explains Sandra Blaise-Boisseau, scientist in the Virology mixed research unit (UMR), at the ANSES animal health laboratory. As there are around sixty strains, for each new emergence it is necessary to know which strain is at the origin.. »
Transport conditions constrained by the contagiousness of the virus
To identify strains, samples must be sent from the areas where sampling takes place to reference laboratories, which have the necessary security conditions to carry out identification analyzes. These laboratories are mainly located in Europe and North America, which may require transporting samples over long distances. ANSES is a reference laboratory on foot and mouth disease for France, the European Union, the World Organization for Animal Health (WHOA) and the Food and Agriculture Organization of the United Nations (FAO). She therefore regularly receives samples to analyze. The transport protocol is strict: “ Samples must be stored in dry ice, respecting the cold chain and using triple packaging to avoid contamination, explains Aurore Romey, from the same Anses Virology UMR. Some countries do not have the means to apply this protocol and refuse to send their samples. We have also had cases where it took several weeks to find dry ice. When we received the samples, they were too altered to isolate the virus. »
An antigen test converted into a transport medium
As part of these reference mandates for WHOA and FAO, ANSES has developed an alternative transport protocol, easy and quick to implement and at a lower cost. The scientists started from the equipment already used when collecting samples in cases of suspected foot-and-mouth disease: “ Antigenic tests, similar to the self-tests used for Covid, are used in the field, explains Sandra Blaise-Boisseau. They make it possible to know in a few tens of minutes if the animals are affected by foot-and-mouth disease but do not indicate the strain in question. We therefore wondered if it was possible to use this test support to transport samples to diagnostic laboratories. »
First of all, the possibility of recovering the virus and identifying the strain from the deposit on the test was confirmed. But the virus being infectious, it is above all necessary to inactivate it in order to transport it. To do this, scientists tested several disinfectants known to be effective against the foot-and-mouth disease virus. Their choice fell on citric acid diluted to 0.2%. The chosen concentration inactivates the virus, making it incapable of infecting cells while preserving its genetic material sufficiently to subsequently identify the strain to which it belongs.
Field test success
This method has been tested in real conditions in Nigeria and Turkey. Pakistan also participated in the trials with samples present in their collections. “ Each country sent us 20 samples. We were able to confirm in the laboratory that it was the foot-and-mouth disease virus in all cases. The serotype involved, which constitutes the first level of characterization of the strains, was identified for 86% of samples. By going further in terms of characterization, the strain could be identified for 60% of the samples. » rejoice the scientists. For some samples, the genome was completely preserved. “ It’s a plus ! To identify strains, fragments of the genome are sufficient. But with complete RNA we were able to do what we call “virus rescue” “. Concretely, it is about produce a live, infectious virus in vitro from its RNA, after having introduced the latter into animal cells. This possibility of having the live infectious virus makes it possible in particular to test the effectiveness of a vaccine against a new strain.
The work was funded by FAO’s European Commission for the Control of Foot and Mouth Disease (EuFMD). The latter has recognized the usefulness of the method when it was not possible to use the standard transport protocol. It commissioned ANSES to test it on other brands of antigenic tests than the one on which the initial study was carried out. Work is underway.
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